Pressure-swing-adsorption (PSA) uses sharp pressure changes within one or more chambers filled with molecular sieve to separate various components in a feed gas. For example, the PSA process may be used in conjunction with zeolite molecular sieve material to separate oxygen and argon from the feed gas. The PSA process is more efficient at separating oxygen from air than other methods (e.g. cryogenics), but it also has some drawbacks. One drawback is that the molecular sieve has a high affinity for water. Water ingestion by the molecular sieve causes a significant drop in gas separation performance. In addition, while many PSA systems include features for removing liquid water that might be present in the compressed air, most oxygen-generating PSA systems do not have a suitable means for drying the compressed air that is fed into the sieve beds. As a result, the sieve beds are typically exposed to some amount of water present in the compressed air.
The two most common methods for removing liquid water upstream of the molecular sieve beds are the use of coalescing filters and centrifugal water separators. Coalescing filters are commonly used in industrial applications and are very effective at removing small liquid droplets from compressed air streams. Coalescing filters work by joining small droplets together to form large droplets that are channeled to a drain for removal from the system. This process may work well for constant air flows, but the PSA process has large swings in air flow through the filter as the sieve beds cycle between separation and regeneration phases. As a result, the cyclical air flow through the filter driven by the PSA process lowers the water separation capability of the coalescing filter to catch small water droplets and combine them into larger droplets. While some of these droplets reach sufficient mass to flow down to the drain, many droplets, unfortunately, get caught in a medium range where they are too small to be overcome by gravity but are also too large to remain on the filter during peak flow through the filter. These water droplets typically come off the filter element and deposit on the inside wall of the filter housing. Some of these droplets may still join together and flow to the drain as desired, but other droplets may slowly migrate towards the filter housing outlet and eventually flow to downstream components.
Centrifugal water separators have also proven to be very effective at removing liquid water from compressed air. These water separators work by directing compressed air in such a way to use inertia to help small water droplets join together and flow to a drain. The major drawbacks for centrifugal water separators are their size and the fact that they are often separate units from the PSA concentrator and must be supported separately.
Thus, there is a need for a coalescing filter for a PSA system with improved water separation capability thereby eliminating the need for a separate centrifugal water separator. The present invention satisfies this as well as other needs.